(i) Field of the Invention
This invention is concerned with prills and their manufacture, more especially the invention is concerned with a water-degradable sulphur prill and its manufacture and with an apparatus which can be used for such manufacture.
(ii) Description of the Prior Art
Sulphur is widely employed as a fertilizer or soil nutrient, since sulphur is essential to plant life and in many areas the soil must be supplemented with sulphur. In alkaline soils, addition of sulphur is desirable to increase soil water intake and aeration, improve the physical condition of the soil, eliminate harmful alkalinity and sodium problems and increase the availability to the plant of elements in the soil necessary for plant life.
Use of sulphur results in improvement in both yield and quality of the crop.
Sulphur is most suitably employed in elemental form and different processes have been proposed for providing sulphur in a form for use as a fertilizer.
Canadian Patent No. 1,054,821, Bob L. Caldwell, issued May 22, 1979, describes a method of producing granular sulphur-bentonite mixture for use as a fertilizer in which a uniform mixture of molten sulphur and bentonite is poured onto a wet thermally conductive metal plate and is allowed to cool to a thickness of 0.25 to 2 inches whereafter the solid is comminuted to provide granules. In U.S. Pat. No. 4,133,669, Bob L. Caldwell et al, issued Jan. 9, 1979, there is described a method of producing a water-degradable solid pellet of bentonite and elemental sulphur in which droplets of a mixture of molten sulphur are allowed to fall into a liquid fertilizer solution to anneal the droplets into pellets. An aqueous liquid fertilizer solution of low water content is used because the sulphur-bentonite mixture does not pelletize in water but rather degrades.
These prior processes, although producing acceptable water-degradable fertilizer products, have certain disadvantages. The granular product produced in accordance with Canadian Patent No. 1,054,821 comprises non-spherical particles of irregular shape having a non-smooth surface. The granules thus have a greater volume when packed for transport than would corresponding spherical particles and thus the transportation costs are higher than they would be for spherical particles. The non-smooth surface of the irregular shaped granules is friable such that the granular product has an undesirable content of fine particles or dust which is herein referred to as "fines". These fines are produced during the manufacture reducing the efficiency of yield of granular product and during subsequent storage, transportation and use of the granular product, particularly when the product is mobile and individual granules rub against each other. The fines are particularly undesirable in that during processing and use of the granules, clouds of dust may be generated in the air which is unpleasant for workers and may be hazardous to health; under certain circumstances there is also a danger of explosion.
In addition the irregular surfaces of the granular product renders the product susceptible to degradation at the surface on exposure to a humid environment, such that the product cannot be stored for long periods and also some degradation may occur during transport.
The pellets of U.S. Pat. No. 4,133,669 are allegedly dust-free, a nitrogen coating on the pellet retarding escape of dust from the pellet, however, the process of manufacture requires the use of a large volume of expensive nitrogen-containing liquid fertilizer to anneal the molten droplets and form the coating. A less costly aqueous annealing medium would be economically advantageous. In addition the pellets formed are not spherical, because the molten droplets are first formed in an air space below a perforation plate, whereafter the preformed droplets fall through the air under gravity into the liquid fertilizer. This results in spheroidal rather than spherical particles, the particles being flattened or oblate spheroids, and such spheroidal particles occupy a larger volume when packed and are thus more costly in storage and transport.
It is an object of the present invention to provide a water-degradable, substantially spherical particle having a hard, smooth surface, for use as a fertilizer.
It is a further object of the invention to provide an improved process for producing a water-degradable sulphur clay particle for use as a fertilizer.
It is a still further object of the invention to provide an improved process for producing water-degradable sulphur-clay prills for use as a fertilizer.
It is yet another object of the invention to provide a method of forming solid, substantially spherical particles from a molten, solidifiable material.
It is still yet another object of the invention to provide an apparatus for forming solid particles and prills from molten, solidifiable material.
The invention also has as an object to provide a prilling head for producing a solid prill from molten material.